1. Field of the Invention
The present invention relates to a fabricating method of a plate, and more particularly to a fabricating method of a printing plate with a fine pattern using an electric field.
2. Description of the Related Art
In general, a liquid crystal display device controls the light transmittance of liquid crystal molecules by controlling their orientation through the use of an electric field, thereby displaying a picture. To this end, the liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in a matrix shape, and a drive circuit for driving the liquid crystal display panel. FIG. 1 is an exploded perspective plan view representing a liquid crystal display panel of the related art. The liquid crystal display panel, as shown in FIG. 1, includes a thin film transistor substrate 70 and a color filter substrate 80 which are bonded together to face each other with liquid crystal molecules 90 therebetween.
The thin film transistor substrate 70 includes: a gate line 71 and a data line 72 crossing each other; a thin film transistor 73 formed at the crossing of the gate and data lines 71 and 72; a pixel electrode connected to the thin film transistor 73; and a lower alignment film (not shown) over the pixel electrode 74 for aligning the liquid crystal molecules 90.
The thin film transistor 73 includes: a semiconductor layer (not shown) forming channel; a source electrode (not shown) connected to the data line 72; and a drain electrode (not shown) facing the source electrode with the channel therebetween. Herein, the semiconductor layer includes an active layer (not shown) which forms a channel between the source electrode and the drain electrode; and an ohmic contact layer (not shown) which is located on the active layer to provide an ohmic contact between the source electrode and the active layer at one end of the active layer and between the drain electrode and the active layer at another end of the active layer.
The color filter substrate 80 includes: a black matrix 81 for preventing light leakage; a color filter 82 for realizing color; a common electrode 83 forming a vertical electric field with the pixel electrode 74; and an upper alignment film 84 over the common electrode 83 for aligning the liquid crystal molecules 90. The alignment film 84 acts to align liquid crystal molecules 90, disposed between the thin film transistor substrate 70 and the color filter substrate 80, in an initial designated direction. Alignment grooves (not shown) along which the liquid crystal molecules line up are formed in the alignment film 84 by a rubbing process wherein an organic film, such as polyimide, is used as an alignment film.
The gate line, the data line, the active layer can be formed on the thin film transistor substrate by a plurality of patterning processes that include the use of masks. Further, the black matrix and color filters can be formed on the color filter substrate with a plurality of patterning processes that include the use of masks. Such patterning processes include many processes, such as thin film deposition, cleaning, photolithography, etching, and photo-resist removal, etc. Thus, a patterning process using a mask has the problem of having a high manufacturing cost due to its complexity. To solve this problem, an off-set printing method of transferring a pattern onto the thin film transistor substrate or the color filter substrate has been developed in which the pattern is printed by a printing plate. The pattern is formed on the printing plate by spreading photo-resist over the printing plate with a roller and then partially curing the photo-resist.
FIGS. 2A to 2H illustrate production process stages of a printing plate in which an isotropically-etched fine pattern of the related art is formed. Hereinafter, referring to FIGS. 2A to 2H, a method of forming a fine pattern on a substrate by an off-set printing method of the related art will be described in detail. First, as shown in FIGS. 2A, a conductive metal layer 12 is formed on a printing plate 11 by a deposition technique, such as sputtering, etc. The conductive layer 12 formed on the printing plate 11 is formed of a conductive metal or combination of conductive metals, such as chrome Cr, molybdenum Mo, copper Cu, and ITO.
Then, as shown in FIG. 2B, exposure and development processes are performed by spreading a photo-resist 20 on the conductive metal layer 12 and using a mask to cure the photo-resist 20 with ultraviolet light so as to form a fine photo-resist pattern on the conductive metal layer 12.
After the exposure and development processes for the photo-resist 20 are performed as described above, a photo-resist pattern 20A exposing a conductive metal layer 12 on the printing plate 11 is formed by removing the exposed portion of the photo-resist 20, as shown in FIG. 2C.
An etching process is performed on the conductive metal layer 12 exposed by the photo-resist pattern 20A, as shown in FIG. 2D.
After the etching process, the entire photo-resist pattern 20A formed on the etched conductive metal layer 12 is removed. Thus, a metal pattern 12A used as an etching-resist when forming a fine pattern on the printing plate 11 is formed, as shown in FIG. 2E.
After forming the metal pattern 12A on the printing plate 11, an etching process is performed on the exposed area of the printing plate 11 using the metal pattern 12A formed on the printing plate 11 as the etching-resist, as shown in FIG. 2F.
As the etching process is performed on the area of the printing plate 11 exposed through the metal pattern 12A acting as the etching-resist, the area of the printing plate 11 is simultaneously etched in both vertical and horizontal directions within the printing plate 11, as shown in FIG. 2G
After the etching of the printing plate 11, the metal pattern 12A acting as the etching resist on the printing plate 11 is removed by another etching process. The pattern 11A etched into the printing plate has a depth D in a vertical direction that is equal to the pattern width W in the horizontal direction, as shown in FIG. 2H.
In the case of forming a pattern in the printing plate 11 by the related art method described above, the printing plate 11 is isotropically etched in both the horizontal and vertical directions as the etching process is performed through the metal pattern 12A acting as the etching-resist, as shown in FIG. 2G Accordingly, there is difficulty in forming a fine pattern 11 A having a pattern width less than the depth of the pattern.